This homebrew set above uses a GE circuit board
almost identical to that in the GE T1290A. Right click "view image" to see the schematic, with my mods, full size.
These mods include a separate AM detector
using a base-collector strapped transistor for better weak signal demodulation, an
RFI filter
on the incoming powerline, and
changing a grounded (with respect to RF) base bipolar
transistor to a grounded gate JFET in the FM RF amp stage; this is to
improve the RF stage to have good strong signal performance, ie, better FM receive dynamic range, ie, a better intercept point. avoiding intermod products.
If you are working on GE radios like this, check
the low value resistors. I had to replace a 100 Ω, a few 150 Ω and a 220 Ω
resistors. They all went flakey. The bad 100 Ω resistor made the FM local oscillator quit at
the lower end of the band. In a few spots, where the circuit board nodes were close together, found it easier to
use the larger sized surface mount resistors to replace the old resistors that were in crowded areas on the component side of the board.
Note the unusual calibration of the AM dial of the homebrew set.
Inside this homebrew set is that RFI filter, and series resistor.
This RFI filter knocks down crud from the powerline. Note, right of the power resistor, the white wire with orange and blue, like Syracuse Orange and Blue.
LW MW SW 250V AC/DC 3 tubes: UCL83, UBF89, UCH81
TRF set: 12BA6 RF, 12AT6 triode detector, 50B5
audio output, 35W4 rectifier.
